Ablative resins used for retarding regression in ablative materia

Burns, E. A.

Kendrick, W. P.

Lubowitz, H. R.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS A N D  S P A C E  ADMIPtlS"$RTlON 
WASHINGTON, D.C. 20546 
8% gc: ; < i;;,J 
REPLY 10 
ATfN OF: G p  
TO r ~ ~ I / ~ c i e n t i £  i c  bc Wchnica l  Information Bivllsion 
Attent ion:  M i s s  Winnie M. Morgan 
FROM: ~ ~ / 0 f f i c e  of A s s i ~ t a q t  General Counsel f o r  
Pa ten t  Matters  
. * 
SUBJECT: Announcement oE NASA-Owned U. S. Pa ten t s  i n  STAR 
I n  accordance wi th  t h e  procedures agreed upon by Code GP 
and Code USI, t h e  a t tached NASA-owned U. S, Pa ten t  is being 
forwarded f o r  a b s t r a c t i n g  and announcement i n  NASA STAR, 
The foblowing in&omat;ion is providedo 
U. S. Pa ten t  No. . . '  8 
Government o r  
Corporate Employee 
Supplementary Corporate 
Source ( i f  app l i cab le )  : 
NASA Pa ten t  C a s e  No. t XEE-059163 
NOTE - If t h i s  p a t e n t  covers  an invent ion  made by a 
of a NASA Contractor ,  the fol lowing is ap 
yes  NO E l  
Pursuant t o  Sec t ion  305(a) of t h e  National Aeronautics and 
Space Act, t h e  name of t h e  Administrator  of NWsA appears on 
t h e  f i r s t  page of t h e  pa ten t ;  however, tlhe name of t h e  aceuah 
inventor  (author) appears at t h e  heading of Col 
t h e  Specification, f o l l w i n g  the words " with reswct to 
~ l i  -'14032 
(ACCEsSlON NUfdBER) (THRU) 
&L. 
(PAGES) (CODE) 
Encahcasure " < & 1 
& -..-."..- L. a- 
Copy of Patent  c i t ed  above 2 crdnsa cw O R  riisix ow AD [QuldBEai (CATEGORYI  
https://ntrs.nasa.gov/search.jsp?R=19710004557 2020-03-17T02:33:29+00:00Z
United States Patent 8Wi 3,490,939 @e Patented Jan. 20, 1970 
3,430,939 
ABLATIVE RESIN 
Myrnan Hi. Lnbowita, Redondo Beach, Eugene A. Burns, 
Palos Verdes Estates, and William P. Rendrick, Mall- 
ltattsn Beach, Calif., assignors, by mesne assignments, 
to tine United States of America as ,represented by the 
Adininish.ator of the National Aeronautics and Space 
Ad~ninistratlon 
No Drawing. Filed May 23, 1966, Ser. No. 551,933 
Int. CI. C23c 11 /02 
U.S. el. 11'7-106 8 Claims 
shock. It has been found ihat the physicai iiicorporalion 
of an alkaline earth metal oxide powder into an ablative 
resin matrix such as an epoxy material for the purpose 
of preparing a shock stable ablator is unsuitable as the 
oxide coating forming on the resin during the ablative 
process will not withstand the erosive action of the 
discharging exhaust gases. The oxide coating forming 
on the ablative surface from the powdered alkaline earth 
metal oxide is subject to undercutting, leading to rapid 
erosion. The chemical binding of the alkaline earth 
metal provided by the acrylate polymer is apparently 
responsible for the superior protective film. This is true 
ABSTRACT 'OF THE DISCLOSURE even where the polyalkaline earth metal acrylate is used 
as one of the several resins of an ablative composite, 
A method and structure for retarding the rate of re- 15 for in with conventional 
gression of an ablative surface by incorporating a ~ 0 1 ~ -  ablative resins as a phenol-formalde.,yde polymer or an 
alkaline earth metal acrylate in the ablative mate~ial. 
epoxy resin. When the ablative material is subjected to high temper- The polyalkaline earth metal acrylate material lnay 
ature gases, the alkaline earth metal acrylate decomposes be hot pressed into neat resin masses of to form a protective oxide coating on the surface of 20 suitable for use in thrust liners and 
the ablative material. comuonents of rocket engines and other high temoer- 
ORIGIN O F  THE INVENTION 
- - 
ature applications. The polymer is fused into a compact 
resin mass by the application of high pressures, for ex- 
ample, in the range-of 15,000 to 20,600 p.s.i. at rela- The invention described herein was made in the per- 25 tively high temperatures in the range of 300 to 4000 C .  
forrnance of work under a NASA contract and is sub- DLlring the heat pressing operation the polymer is desir- ject to the provisions of Section 305 of the National 
ably maintained in an evacuated atmosphere, The neat Aeronautics and Space Act of 1958, Public Law 85-568 
mass may be machined into useful objects, It has been (72 Stat. 435; 42 U.S.C. 2457). found that the polycalcium acrylate resin is the tough- This invention resins and 'lore 30 est of the alkaline earth metal acrylate polymers. The particularly to polynleric alkaline earth metal aery- nlagnesium version of the polymer is generally the most late% and a composition containing the polymer and 
suitable as an ablative resin because it provides the great- process for retarding rate of regression of an ablative 
est retardation of the rate of regression of an 
sul-face exposed to high temperature gases. surface. Ablative resins employed for the fabrication of rocket 35 The polyalkaline earth metal acrylates are desirably 
nozzles and the like have typically been produced from prepared by a free radical catalysis of an alkaline earth phenol-formaldehyde resins and epoxy resinous mater- metal acrylate monomer dissolved in water. The free ials. The conventional materials while exhibiting desira- radical catalysis may be initiated by various ones of the ble thermal shock characteristics ablate rapidly and lead known organic and inorganic peroxides such as: 
to early dimensional instability of the ablator structure, 40 
particularly in fluorine/hydrogen combustion gas product Di-t-butyl peroxide; 
environments. 2,5-dimethyl-2,s-bis(tertiary butylperoxy) hexane; 
It is a principal object of the invention to provide an n-Butyl-4,4-bis(tertiary butylperoxy) valerate; 
improved ablative resin and resinous composites con- 2,5-dimethyl-2,5-bis(tertiary butylperoxy) hexyne-3; 
taining such material. Tertiary-butyl perbenzoate; 
It is another object of the invention to provide an Hydrogen peroxide. 
ablative resin which in the presence of high tempera- The polymerization is generally carried on at a tempera- 
ture exhaust gases forms a relatively stable oxide pro- ture in the range of 100 to 105" C. and the peroxide is 
tective coating. supplied in an amount of 0.001 to 1.0 part by weight per 
It is a still further object of the invention to provide 50 part of the monomer. The polymer product of the reac- 
a process for retarding the rate of regression of an abla- tion will precipitate out of the water. The polymer is then 
tive surface exposed to high temperature gases. isolated and dried to an anhydrous condition. Desirably, 
Polyalkaline earth metal acrylates have been found the anhydrous polymer is finely ground to facilitate its 
to have exceptionally superior ablative qualities and use in the fabrication of an ablative structure. Where the 
unlike ablative resins proposed heretofore will in the 55 acrylate resin of the invention is incorporated in a resin 
presence of high temperature exhaust gases decompose corfiposite it has been found permissible to employ the 
to form a contin~~oas protective coating of an oxide on alkaline earth metal acrylate polymer in a minor amount 
the exposed surfaces. Alkaline earth metal acrylates ex- of the total resin, say 20-60% by weight, with a conven- 
hibit an exceptionally high stability and have been found tional ablative resin such as an epoxy resin or a phenol- 
to retard significantly the rate of regression of an abla- 60 formaldehyde resin being preseilt in a predominant 
tive surface in which they are incorporated. The dimen- amount. 
sional stability of the ablaior is thus prolonged by the It is established by infrared spectomell-y that the vinyl 
fo~.niaiion of the coating. At the high tempel-zture of group is absent from thc polymer and ih::t there i s  an 
the discharge gas of a rocket engine, the protective oxide oxygen-metal bond. Further compositional analyses con- 
coating takes the form of a molten film. 65 firm that two acrylic molecules exist in the polyalkaline 
The alkaline earth metal acrylate polymers exhibit par- earth metal acrylate composition per one lnetal atom. 
titularly superior resistance to the combustion prodocts 
of a fluorine/hydrogen propeilent combination. The EXAMPLE I 
acrylate resin is sttbstantially insensitive to thermal Calcium acrylate monomer is prepared by the following 
shock. In contrast, the oxides of alkaline earth metals 70 procedure: Dissolve 72.06 parts acrylic acid (M.P. 12-14" 
per se, may not be used as ablators because they, as C . )  in 500 parts water. Transfer slowly 55.05 parts calcium 
ceramic materials, are friable and sensitive to thermal carbonate to the acrylic acid solution. Stir the solution 
3,490,939 
3 is 
continuousiy drrring nddition of the calcitirn carl;o::nte anci izxAM?i.E: 
for a period of 4 Elours after addition. A!low Ihc unrsacted The polybal.ium acryl~ite is prepared in the following 
calciuin carbonate to scitlc orit of solulian arid filter Ihz nla,lncr: tqfulix 72 acrylic acid (M,P. 12--140 c.1 witll 
supernatant licluid. Pl.ecipita.te the calci~im acrylate mono- 500 Slowiy parts barium 
mer froni tile fi1:ered supernataiit liquid by an addition of into the solution and continue mixing for 4 holIrs, ~ l l ~ ~  
an equal volume of acetone. Filter the precipitate and wash the unreacted barium carbonate to and then filter the 
three times with acetone. Then dry overnight at 90" G. supernatant liquid. Transfer the filtered bariurn acrylate 
Polycalciucl acrylate is prepared by the following Proce- monomer solution to a distillation flask equipped wi!h a 
dure: ~ r a n s f e r  10 parts of the dried calcium acrI'late stirring apparatus. Bring the solution to boiling and reflux 
monomer to a distillation flask containing 100 parts water lo for minutes with stirring, ~ d d  4 drops of t-butyl per- 
and a stirring apparatus. Stir the solution until well mixed benzoate and continue refluxing for an additional 10 
and then heat to boiling and reflux for 10 minutes. Add 2 cool  the flask to room temperature and remove 
drops of t-butyl perbenzoate per 100 ml. of solution and the white, rubber-like polybarium acrylate. Wash the pre- 
continue refluxing for an  additional 10 minutes. Allow cipitate three times with water, dry it overnight at 1000 c., 
the flask to cool to room temperature and then nlanually 15 and then grind to pass a 200 mesh sieve screen. The poly- 
remove the white rubber-like polycalcium acrylate. Wash bal.iunl acrylate monohydrate and dihydrate are 
the precipitate three times with water, dry it overnight at forms of the polymer in air. 
100" C. and then grind it to pass a 200 mesh sieve screen. We claim: 
Hard compact masses of polycalcium acrylate are pre- 1. A process for retarding the rate of regression of an 
pared in the following manner: The material is transferred 20 ablative surface exposed to high temperatire gases, said 
to a hot vacuum press and subjected to the following con- process con,prising: 
ditions for a period of 30 minutes: 15,000 p.s.i., 350" C.,  providing an ablative structure containing a fused poly- 
and vacuum of about 1 torr. The resultant product is a alkaline earth metal acrylate; and 
hard white homogeneous material having a density of exposing the surface of the ablative structure to high 
1.858 g./ml. The pressed polycalcium acrylate is insensi- 25 temperature gases 
tive to the thermal shock imposed by an oxygen-hydro- sufficiently hot to decompose said polyalkaline earth 
carbon and fluorine-hydrogen flame. The ability of this melal acrylate whereby a continuous oxide filnl of 
material to withstand a 10 second exposure of a fluorine/ said alkriline earth metal io~- r i~s  on said surface to  
hydrogen flame was determined by measurement of the protect same. 
volume loss which took place on exposure for 10 seconds 30 2, A process in accordance claim 1 wherein the 
to a fluorine/hydrogen flame at a volnnle ratio of 1.0 and polyalkaline earth acr)ilate is from the 
located 1.25 inches from the torch tip. The volume loss of consisting of polymagnesium acrylate, polycalcium 
the polycalcium acrylate was 0.16 ~ m . ~ .  Comparable phe- acrylate, and polybarium acrylate. 
nolic resins (Monsanta SC-1008) had a voltln~e loss of 3. A process in accordance with claim 1 wherein the 
0.3 1 cm.3 when subjected to a similar test. 35 ablative structure is a resin composite having the poly- 
alkaline earth metal acrylate present with a second heat 
EXAMPLE I1 ablative resin selected from the group consisting of a 
phenol-formaldehyde resin and an epoxy resin. 
An alternative procedure for the preparation of poly- 4. A process an accordance with claim 1 wherein the 
calcium acrylate is described below. 40 ablative structure contains the polyalkaline earth metal 
Transfer 10 parts of the powdered calcium acrylate acrylate as the sole resin. 
monomer prepared in Example I to a distillation flask con- 5. An  ablative structure comprising a resin mass con- 
taining 100 parts acetone and a stirring apparatus. Heat taining a fused polyalkaline earth metal acrylate and 
the solution boiling with continuous vigorous stirring. Add 45 having a surface thereof continuously covered by an 
4 drops of t-butyl perbenzoate per 100 ml. of solution and oxide of said alkaline earth metal, said oxide being 
then reflux for a period of 30 minutes. Cool the flask to intergrally bonded to said ablative structure. 
room temperature and retrieve the precipitate in the flask 6. An ablative structure in accordance with claim 5 
by filtration. Wash the solid material in water, then dry wherein the resin mass is a neat resin mass of the poly- 
and grind it as described in Example I. alkaline earth metal acrylate selected from the group 
Compact resin masses can be prepared in a manner consisting of polymagnesium acrylate, polycalcirim acry- 
similar to that described in Example I. late, and polybarium acrylate. 
7. A n  ablative structure in accordance with claim 5 
EXAMPLE I11 wherein the resin mass comprises a con~posite of the 
55 polyalkaline earth metal acrylate and a second heat 
The  polymagnesium acrylate is prepared in the follow- ablative resin selected from the group consisting of a 
ing manner; Mix 72 parts acrylic acid (M.P. 12-14" C.)  phenol-formaldehyde resin and an epoxy resin. 
with 500 parts water. Slo~vly add 55 parts magnesium 8. An  ablative structure in accordance with claim 5 
carbonate into the solution and continue mixing for 4 wherein the pa1)~alkaline earth metal acrplate contains 
hours. Allow the unreacted magnesium carbonate to settle (jo one metal atom per two acrylic moIecules. 
and then filter the supernatant liquid. Transfer the filtered 
magnesium acrylate monomer solution to a distillation References Cited 
Aask equipped with a stirring apparatus. Bring the solution UNITED STATES PATENIS 
to boiling and reflux for 10 minutes with stirring. Add 4 
drops of t-butyl perbenzoate and continue refluxing for (35 3,377,213 4/19hR Hiller 117-1 18 X 
an additional 10 minutes. Cool the flask to room teinpera- FOREIGN PATENTS 
ture and reniove the white rubber-like polymagnesirrm 1,367,994 France. 
acrplate. Wash the precipitate three times with water, d ry  
it overnight at 100' C. and then grind it to pass a 200 WILLIAM D. MARTIN, PrimarJ1 Examiner 
mesh sieve screen. The polymagnesium acrylate mono- 70 
hydrate and dihydrate are hygroscopically stable in air. J. E. ICIILLER> J''.~ Assistant 
The anhydro~is polpn~er increases its weight in air to a 
value which corresponds to that expected for the monohy- E.S. C1. X.R. 
drate. 117-1 18, 138.8; 60-271; 102-105: 260-844 


Ablative resin Patent

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server